The NHIS is a large, annual population-based health survey conducted by the National Center for Health Statistics. The NHIS is the principal source of information on the health of the civilian, non-institutionalized, household population of the United States. It has been conducted continuously since its inception in 1957. The NHIS is currently designed to over-sample the black, Hispanic, and Asian populations. Since the most recent sample redesign was implemented in 2006, the maximum numbers of interviewed families and persons have been about 35,000 and 87,500, respectively. However, in recent years, this number has fluctuated due to funding.